1. Field of the Invention
The present invention relates to an ink supply mechanism in an electrostatic ink jet recording apparatus and in particular, to an ink supply mechanism for use in a serial type electrostatic ink jet recording apparatus.
2. Description of the Related Art
For example, Japanese Patent Publication (unexamined) A7-76105 discloses an ink chamber pressure regulating means for use in an ink jet recording apparatus using a liquid ink as a recording material.
This ink chamber pressure regulating means includes a pressure regulating valve having a slit in an elastic member. When the pressure difference between the inside and the outside of the ink tank increases, the elastic member is greatly deformed to open the slit so that the interior of the ink tank communicates with the atmospheric air so that the pressure in the ink tank increases up to the atmospheric pressure, thus regulating the pressure in the ink tank.
Moreover, Japanese Patent Publication (unexamined) A61-112648 discloses a printing head including a pressure regulating path pipe having a first end communicating with the ink changer and a second end closed. A pressure change in the ink chamber is absorbed by a volume change of a closed air layer.
However, the aforementioned devices have various problems as follows.
The first problem is efficiency of absorbing the pressure fluctuation.
The pressure regulating device should rapidly absorb a shock type pressure change when one has occurred, so as to maintain a predetermined inner pressure of the ink chamber. The shock type pressure is caused by high-speed ink movement in the ink chamber in the main scan direction (first reason) or by a pressure fluctuation generated from an ink circulation member such as a pump (second reason). In the aforementioned configuration having a closed air chamber, it is difficult to sufficiently absorb the pressure fluctuation caused by the second reason.
This is because the ink chamber communicates with the ink circulator and a pressure wave is transferred in the fluid.
That is, in order to effectively absorb these pressure fluctuations, it is preferable that the ink in the ink chamber be disconnected as a fluid from the ink in the ink circulator.
The second problem is that these pressure regulating means are intended for the ink almost in a still state. Most of the conventional ink jet printers do not need an ink circulation, and for the ink discharged from a nozzle, a new ink is added by the capillary effect or mechanical force. These methods can perform pressure adjustment. However, in an ink jet printer of serial type in which the ink continuously circulates, it is difficult to maintain a predetermined pressure, and ink circulation may be disturbed.